Public safety agencies around the world are considering the deployment of broadband bearers such as LTE for improving data connectivity in their radio systems. Utility industries such as electricity distribution are also looking to exploit similar technology. The expectation is to deploy this relatively wideband technology to operate in parallel with existing narrow band systems such as P25. In the United States, the FCC has made specific frequency allocations supporting this model of deployment.
The LTE standard is based on OFDM (Orthogonal Frequency Division Multiplexing) of subcarriers and can be deployed in a number of channel bandwidths. A typical LTE FDD (Frequency Division Duplex) mode has uplink/downlink pairs including bandwidths of 20 MHz, 15 MHz, 10 MHz, 5 MHz, 3 MHz and 1.4 MHz. In the United States assignments of spectrum have been made representing 10+10 MHz in 3GPP band 14 for broadband operation. Specifically, the US has assigned frequencies 758 MHz to 768 MHz paired with 788 MHz to 798 MHz for broadband operation using LTE for Public Safety use. In addition, an assignment has been made for Public Safety for narrow band operation from 769 MHz to 775 MHz paired with 799 to 805 MHz. In other parts of the world private broadband assignments are being considered for use by public safety and critical infrastructure.
LTE coverage is made up of a number of frequency blocks, also referred to as resource blocks. An FDD 5 MHz channel has a set 25 resource blocks where each block is 180 kHz. Collectively the set of 25 blocks produces a bandwidth of 4.5 MHz within the 5 MHz channel with the 0.5 MHz remainder being used to contain the spectral skirts that operate within regulated emission masks. The channel is further divided into timeslots each of 0.5 ms, where a collection of 20 slots defines a frame. A resource block is therefore a block extending over a period which may include many timeslots. A set of frequency blocks contains many frames.
Each bearer in a wireless communication system requires a network of base stations to provide the channels over which users can communicate. The base stations are geographically located to provide coverage over a wide area within which the users are expected to move and require voice or data services. The users typically employ hand held or vehicle mounted terminals to communicate with the base stations. Each network generally includes a scheduler or controller which determines the timing and pathway of calls through the network. Bearer networks send control messages which are interpreted by the user terminals, in addition to voice and data messages which are sent between the users. In a trunked radio system a relatively large number of users share a relatively small number of frequencies, without being assigned to a fixed frequency for the duration of each call.